1. Field
Embodiments of the present invention relate to a switching power source.
2. Related Background Art
In some switching power sources, a first N channel MOS transistor and a second N channel MOS transistor are provided between a positive electrode and a negative electrode of a DC voltage source. In such a switching power source, the first N channel transistor and the second N channel transistor are alternately placed in conducting state by controlling gate voltages that are applied to the first N channel transistor and the second N channel transistor, respectively.
In such a switching power source, the gate voltage is applied to the gate terminal of the second N channel transistor with reference to the voltage of the terminal that is connected to the negative electrode. The gate voltage is applied to the gate terminal of the first N channel transistor with reference to the voltage at a midpoint between the first N channel transistor and the second N channel transistor.
However, the midpoint is connected to neither the positive electrode nor the negative electrode of the DC voltage source. Therefore, the voltage at the midpoint fluctuates. In conventional switching power sources, accordingly, the gate voltage is applied to the gate terminal through a photocoupler or a transformer, for instance as disclosed in Tamotsu Inaba, “Pawa MOS FET katsuyo no kiso to jissai (Fundamentals and practice of power MOS-FET use)”, 6th edition, CQ Publishing. Co., Ltd., Feb. 1, 2010, page 136.